Conventional press systems use flywheels, hydraulics or pneumatics to slowly push or force tools through a material, or work. These methods often cause distortion, burrs, inconsistent quality due to their slow velocity pressing. These systems cannot achieve a high impact velocity because of their drive systems. Hence, these slow moving presses usually require lubricants, frequent maintenance and tool replacement or sharpening.
Typical punching operations undergo three phases: elastic, plastic and fracture. In the elastic phase, the work stretches around the tool being pressed into it. The slower the punch moves, the more the work will stretch. The elasticity of the materials is particularly noticeable when punching work that is plastic or rubber, in that these materials will deform around the tool being pressed into them.
In the plastic phase, the work will begin to form small sections, or strings. These strings will be the only portion of the work still connecting the punched portion, or finished pieces, to the non-punched portion, or scrap pieces. Again, this phase is particularly problematic when punching rubber or plastic work materials.
When the strings begin to tear from the finished piece, the fracture phase has begun. As the punch pushes further through the work, each string will rupture, eventually resulting in a freed finished piece. However, the relatively slow impact velocity resultant when using a press with a flywheel, hydraulic or pneumatic drive system can cause significant problems with the finished piece.
A significant problem with mechanical presses is the overall size of the punch press machine. Manufacturers may find it difficult to orient the supplemental equipment that is typically associated with pressing functions, such as a hanging roll feed and/or straightener. Additionally, the tooling used in a mechanical press cannot be removed easily. Hence, when the tool must be replaced or sharpened, a significant delay is interposed in the pressing operation. When the press operations are moving at 20 strokes (presses) per minute, any lengthy delay can become quite costly.
Another problem associated with mechanical presses is the creation of burrs on the finished piece. During the plastic phase, the finished piece is still connected to the scrap piece by strings. When these strings rupture, a small amount of the string, or burr, is left on the edge of the finished piece. A significant amount of burrs can result in malformed finished pieces, which may need to be smoothed, or discarded. Burrs can be significantly problematic when punching plastic and/or rubber work materials, as these materials have high elasticities. One problem associated with burr creation is rolled edges. Due to the heat generated over a relatively long amount of time because of slow impact velocity, the edges of the finished piece may be rolled upwardly around the edge of the tool performing the press.
Tool life and sharpening are also factors that are considered in punch press operations. With mechanical punches performing around 20 strokes per minute, the tool, or dieset, will begin to lose its sharp edges. A misshapen tool can result in increased burrs and particulates, and may lead to disposal of an unsatisfactorily finished piece. When this occurs, the manufacturer must not only discard the substandard finished pieces, it must stop the pressing process and replace or sharpen the tool. Due to a slow dwell time (time between presses) inherent with mechanical presses, any stoppage in the pressing process can be exceedingly costly.
Punch presses can be used in the manufacturing process for integrated circuits. In this manner, the punch press may be used to punch the PC boards used for the integrated circuits. Alternatively, the presses may be used to stamp flexible, plastic separators used in green ceramic processing. The stamping usually occurs in s clear room, and thus, it is extremely important that the process produce no particulates or burrs.
With the above-mentioned disadvantages in mind, electromagnetically driven punch presses have been developed. An electromagnetic drive system can significantly increase the impact velocity from the prior mechanical presses. An increased velocity of the tool can overcome the disadvantages of the mechanical presses, primarily by effectively eliminating the time the work spends in the elastic and plastic phases. Without expending time in these phases, the press takes the work directly to the point of fracture, eliminating burrs, rolling, and other problems associated with slow, mechanical presses. However, with decreased dwell time, electromagnetic presses can operate between 20 and 400 strokes per minute. At this rate, heat can build up and cause the resistance, exemplified by the solenoid, to increase. If the current to the solenoid is not increased, the press will operate slower, embodied in slower dwell time and/or slower impact velocity. In either situation, work material may be wasted, or the press may have to be cooled, which can present a significant delay.
One such electromagnetic press is described in U.S. Pat. No. 5,113,736 to Meyerle. Meyerle '736 teaches a punch press electromagnetically driven by a solenoid winding. When energized, the solenoid winding pulls an armature through the winding space. The armature presses a tool into a piece of work material, and completes the punch. The armature's impact is absorbed by a series of urethane stoppers, and is returned to its start position by a series of springs, which are connected to the tool. The press taught by Meyerle '736 contains several methods for manually adjusting the stroke length of the tool, due to work material thickness, tool height reduction due to sharpening, and various other reasons. These adjustments are static, in that they cannot be performed in real-time while the press is operating. The current to the solenoid must be discontinued, and the adjustments must be made to several portions of the press before re-starting the press. It can be undesirable to be unaware of the real-time functional conditions of the press while it is operating. For example, if the press velocity begins to slow, the same problems that are inherent in mechanical presses may begin to arise. Hence, a device used to provide real-time updates to conditions such as velocity and dynamic positioning of the press can provide useful advantages.
Another electromagnetic press is described in U.S. Pat. No. 6,484,613 B1 to Lee et al. Lee '613 teaches a press that applies a current to a solenoid to force an armature into a piece of work material. However, to restrain the recoil effect of the armature, a second current is applied to break the armature. While breaking the armature may be advantageous is limiting the recoil effect, this method does not compensate for any real-time updates of the press's operating conditions. Hence, an operator or manufacturer may only have the capability to turn the press on; however, if the press should begin to slow and cause malformed finished pieces, the operator will not be notified of such an event until after the pieces have been formed, which is costly and wasteful.
There presents a need for a device which can provide the operator/manufacturer with important information regarding impact velocity, dwell time and tool positioning, while the press is operating.